JS generates random numbers within a certain range [detailed explanation of four situations]_javascript skills

Foreword:

JS does not have a ready-made function that can directly generate random numbers in a specified range.

But it has a function: Math.random() This function can generate a random number in [0,1).

Using it, we can generate random numbers within a specified range.

When it comes to range, there is a problem of boundary values. This includes four situations:

1) min ≤ r ≤ max (generally this is more common)

2) min ≤ r < max

3) min < r ≤ max

4) min < r < max

1. min ≤ r ≤ max

function RandomNumBoth(Min,Max){
      var Range = Max - Min;
      var Rand = Math.random();
      var num = Min + Math.round(Rand * Range); //四舍五入
      return num;
}

2. min ≤ r < max

function RandomNum(Min, Max) {
      var Range = Max - Min;
      var Rand = Math.random();
      var num = Min + Math.floor(Rand * Range); //舍去
      return num;
}

3. min < r ≤ max

function RandomNum(Min, Max) {
      var Range = Max - Min;
      var Rand = Math.random();
      if(Math.round(Rand * Range)==0){       
        return Min + 1;
      }
      var num = Min + Math.round(Rand * Range);
      return num;
}

4. min < r < max

function RandomNum(Min, Max) {
      var Range = Max - Min;
      var Rand = Math.random();
      if(Math.round(Rand * Range)==0){
        return Min + 1;
      }else if(Math.round(Rand * Max)==Max)
      {
        index++;
        return Max - 1;
      }else{
        var num = Min + Math.round(Rand * Range) - 1;
        return num;
      }
 }

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